In the automotive industry, actuators are used for a number of purposes, including in drivetrain systems such as differentials, axle disconnect systems, or power transfer units. As just one example, typical all-wheel drive systems for vehicles push torque through a torque coupling to the secondary axle to provide enhancements in performance, handling and mobility. These systems require that the secondary axle, and the rest of the driveline, be continually rotating at road speed, which reduces the overall efficiency of the vehicle, and reduces fuel economy.
Secondary axle disconnects are available and they permit the secondary axle and prop shaft to stop rotating. These disconnect systems increase vehicle efficiency, but the current systems also require power to both engage and disengage the output and/or remain engaged or disengaged. The latter situation may require constant power to the system, which reduces overall system efficiency, or may require the use of permanent magnets.
As is known in the art, the actuator converts electrical current into mechanical force. The flow of electrical current into the actuator creates a magnetic field that moves a metal armature which, via additional mechanical elements, results in a change in the engagement/disengagement status of the particular drivetrain system, such as the axle disconnect system described briefly above.
Traditionally, when the actuator was energized, the armature would be drawn towards the solenoid as a result of the magnetic field generated, engaging the axle disconnect system. If it was desirable to keep the system engaged, either current would have to be continually applied or permanent magnets would have to be included in the design of the actuator so that the armature would stay in the engaged position. For obvious reasons, it is not desirable to have a solenoid draw significant power when holding the system engaged (or disengaged).
Latching solenoids may also accomplish maintained engagement with a permanent magnet in the system. The use of permanent magnets has undesirable consequences such as temperature demagnetization and shock demagnetization. In addition, depending on the material, permanent magnets can be costly, difficult to fasten, and can be fragile.
It would be desirable for a system to maintain vehicle efficiency by using an actuator that did not require continuous power or permanent magnets to stay engaged.
The current disclosure utilizes certain design features, certain low cost magnetic steels, and a connect/disconnect strategy that will control current to the actuator. It does not use any separate permanent magnet component(s), thus achieving the same desired result with no design sacrifices or additional cost.